1. Field of the Invention
The present invention relates to laser marking and texturing, particularly forming at least semi-permanent or erasable indicia on one or more materials of a microelectronic device. The materials may include semiconductor substrates, thin films, metallization, and dielectric layers. One or more embodiments may also be applied for forming indicia on MEMs, optoelectronic devices, or biomedical microchips. Various embodiments are useable for various micromachining or microfabrication applications.
2. Background Art
Prior to 1999, Silicon wafer marking was used for identification at wafer level. Initially driven by the Known Good Die, and more recently by traceability and component identification, laser marking on the backside of the wafer at the die level has become the trend, and applied to various packaging technologies, including MCM, Flip Chip, DCA, and CSP. For the past years, research and development effort occurred to develop such a marking tool for production.
One of the emerging challenges for die marking is the recent introduction of very thin wafers. Previously, wafer thickness specifications of 300 to 700 microns (μm) were typical. Present requirements for smaller die, both in terms of area and thickness, are resulting in wafers as thin as 150 μm. Long-term projections are for wafer thickness to be reduced to a feasible limit.
Another challenge is the continuing shrinking of die sizes. For example, die used in DCA (Direct Chip Attach) applications are in the 3 mm to 8 mm dimension. However, products like the RFID tags can be as small as 0.3 mm yet require much of the same information that is included in large die marking. This trend creates the need for further development in die marking to shrink the actual alphanumeric character sizes.
Traditional wafer marking systems are not well suited to present and emerging requirements.
Valuable advancements have been demonstrated, for instance as disclosed in published US Patent Application Number 2003/0060910 entitled “High Speed, Laser-Based Marking Method And System For Producing Machine Readable Marks On Workpieces And Semiconductor Devices With Reduced Subsurface Damage Produced Thereby,” assigned to the assignee of the present invention, published 1 Apr. 2004. However, there is a need to produce high contrast indicia while providing for decreased feature sizes—and to form indicia on microelectronic materials, known to have widely varying optical properties.
Desirable advancements for precision laser marking systems includes: increasing mark density (e.g., smaller effective dot size or line width), control over the marking depth, and improved mark repeatability with control of or substantial elimination of a heat affected zone. There is a need for improvement of readability (e.g., mark contrast with the background), preferably, angle independent contrast.
The ideal mark will be formed with little or no material removed, and will provide contrast that will survive through one or more subsequent fabrication steps. Further, shrinking sizes are expected to mandate increasing density requirements, for instance, font sizes less than 0.3 mm and decreased font spacing.